Electric-discharge device and cathode



May 17, 1960 K. J. GERMESHAUSEN ET AL 2,937,301

. ELECTRIC-DISCHARGE DEVICE AND CATHODE Filed April 25, 1956 INVENTORS KENNETH J. GERMESHAUSEN y SEYMOUR GOLDBERG ATTORNEYS United States Patent 2,937,301 U ELECTRIC-DISCHARGE DEVICE AND CATHODE,

Kenneth J. Germesh'ausen, Newton Center, and Seym'our Goldberg, Lexington, Mass., assignors to Edgerton, Germeshauseu & Grier, Inc., Boston, Mass., a corporation of Massachusetts 7 Application April 25, 1956, Serial No. 580,551

13 Claims. Cl. 313-212 The present invention relates to electric-discharge devices and cathodes therefor, and, more particularly, to improved cathode structures for use in gaseous-discharge tubes and the like.

Various approaches have been proposed for solving the problem, particularly associated with high-power gaseousdischarge devices and the like, such as hydrogenthyratrons that switch, pulse or key high-voltage circuits, of providing a cathode of small physical dimensions that, nonetheless, has a large electron-emissive surface area. Several types of cathode configurations have been evolved to try to accomplish this end, including the utilization of a plurality of parallel cathode-element electron-emitting surfaces disposed within a cup.

It has been found, however, that all'portions of such cathode elements do not actually effectively emit electrons toward the anode of the discharge device at the instant-that a sudden electrical discharge is initiated in the switching or keying circuits, before mentioned, and is applied to the discharge device. Once such an electrical discharge is initiated, the current flowing between the anode and cathode rises very rapidly to its final value; but, since a finite time is required for the plasma to penetrate to all regions of the cathode, most of the electrons are drawn from the portion of the cathode nearest to the drawn from the cathode, whereby most of the currentcontinues to be drawn from those portions of the cathode nearest to the anode. improved operation can be had with cathode elements of limited length, the emitting surfaces of which are more uniformly utilized. A preferred substantially optimum length L of cathode element has been selected that represents a compromise between theprovision of a large electron-emissive surface area and the effecting of more We have found, accordingly, that uniform utilization of the cathode-emitting surface.

That-length L, measured in the direction between the cathode and anode, is given substantially by the following equation:

l t -a) where R is the specific resistance at the electron-emitting surface, having a nominal value'of four ohm-centimeters squared; i is the total current discharged'cumulatively' to the .anode in the dis'charge device; E is the electrical fieldinthe plasma'between the anode and the cathode,

havinga nominal value .of fourteen volts per centimeter; V is the potential drop across-the cathode sheath;

2,937,301 Patented May 17, 1960' is the potential gradient in the cathode sheath with a nominal value of -7 volts per square centimeter; and P is the total perimeter of the cathode in a plane substantially parallel to the surface of the anode.

We have therefore heretofore proposed the utilization of cathode elements having the above length or height L provide a new and improved cathode that eliminates the necessity for a separate heater winding for each of the cathode elements and that provides for a greater uniformity in temperature variations over the complete cathode area.

A further object is to provide an improved cathode structure that inherently is capable of providing greater electron-emissive area than the above-described cathodes. A further object is to provide a new and improved electric-discharge device operating with such an improved 7 cathode.

Other and further objects will be explained hereinafter and will be more particularly pointed out in the appended claims. In summary, however, the present invention resides in the provision of a cathode comprising a base member carrying a plurality of spaced vanes each having electron-emitting surfaces extending along a direction away from the base member, with the base member alone provided with heating means for uniformly heating all of the cathode-vane elements. Preferred constructional details are hereinafter explained.

The invention will now be described in connection with the accompanying drawing, Fig. 1 of which is a longitudinal section of an electric-discharge device embodying the invention in preferred form;

Fig. 2 is a perspective view, upon an enlarged scale, of a portion of the cathode of Fig. 1; and

Figs. 3' and 4 are similar views of modified cathode constructions.

Referringto Fig. 1, an electric-discharge device, illustrated as of the thyratron type, comprises a sealed envelope'21 containing an inverted cup-shaped anode 1, a

control-grid cylinder, fragmentarily illustrated at 3 as provided with a plurality of apertures 5 in line'with the anode 1, and a cathode 2. The envelope 21 may be of cathode 2 is contained within an upwardly disposed conductive cup 9 containing a flat, hollow base member 11.

The base member 11 is in electrical contact with the cup 9 and an external heat-radiation shield 7, the upper inward peripheral projection 50 of which serves also as a sputter shield." The base member 11 supports or carries upon its upper surface a plurality of thin substantially planar conducting vanes 13, 15, 17, etc., welded or otherwise secured to the upper surface'of the base member 11. These vanes 13, 15, 17, etc. are shown confined -'within" the cup 9 and extending toward the upper opening of thecup 9 along the direction from the cathode 2 to the-anode 1, substantially perpendicular or normal to the upper be employed. Though the vanes are shown of substantially' rectangular peripheral shape, moreover, they may also assume. other configurations, as hereinafter described.

Within the hollow of the base member 11 is disposed a continuous heater-coil winding 19, preferably uniformly arranged to establish "substantially. uniform heating: along the upper surface of: the base member 1-1: Thelateral flat. surfacesofthe; thin vanes 13, 1'5; 17, etc. are coated with electron-emissive material;

The anode 1 may be supportedwithin the envelope 21 by awire 23 which may extend througha seal 25 at the top; of the envelope 21 to provide an external anode terminal for connection to the positive terminal of a source of;voltage:in .a suitable well-known pulsing or other circuit: hereinafter: discussed. Thecathodc structure 2 mayhesupportemby conductive strut members 27 and 39xwhich connect to terminal posts-31 and 533, respectively, extending throughthere-entrant glass press 35 at the base of the envelope .21. Negative potentialmay be appliedtolthe cathode Zthrough external conductors 37 that communicate with the terminal posts 31. and 33. The, endsof the heater winding 19, not shown, may be connectedito supportingconductors 39 and 41 which extend to terminal posts.43 in the press 35 to receive heater currentfrom theexternal leads 47. The heater winding may be: maintained at cathode potential by means of the diagonal conducting strut 49 between the conductor 39 andthegconductor 29. A suitable circuit for operating this, discharge device isv disclosed, for example, in United States Letters Patent NO; 2,592,556, issued April 12, 1952, tolennethl. Germeshausen, and in which a source of; highvoltage is discharged between the anode 1' and cathode 2 under the control of an impulse fed to the idi- With the -aid, of theaboveconstruction, but a single heater isrequired for-all'ofthe cathode-emitting surfaces of the vanes13, i5, 17,.etc. This permits the vanes to. beextremely. thin, say, of the order of 0.02 inch in thickness, and-;hence permits the utilization of a large number of, vaneswithin a small cathode cup, resulting in a very large. effective electron-emitting, surface area. A very much. greater, effective cathode-emitting surface area can thereby be obtained than with the aid of individually heatedcathode elements. The vanes, furthermore, may be very closely spaced from one anoth r, with spacings of; the; order offrom: 1, to-2 millimeters, more or less. Since, as before stated, the-topportions of the cathode vanes; are closer, to the anode 1, they will normally emit more electrons thanthelowerportions of the vanes. In accordance with the present invention, however, the heating is effected at the bottom of the vanes so that'the lower portion ofthe vanes will be-heatedmore than the top portions.- Thefreetop portions, in addition, canmore rapidlydissipate heat. This temperature variation along the; vanes is thus the inverse of the electron-emission. tendency. and}te-nds to-cornpensate for; the same, providingmoreuniformemission completelyover the surfaces cathode. Thestructure of the present invention, moreover,;in view of, the solidconnection of the vanes tothe base member; 11 and the utilization of the; single heater inding; 1.9-inthe a e member 11. ismor gge than. thet-before described prion-art cathode structures.

e preferred n t ereigh f eyane n he direction fromthebase member 11 to the an de-1, hasbeforeheen; discussed. Since; this; length'or heightds, pt mal sp ssib1e c ns nt... with ,t eabove-menione limitat ons; it sdesira l in; or er: o; o ain. resr missien su fac rea, t at h her. dimension-of; the; vanes; namely, what; might be; termed; the, width of; e fin s:a ro sz hez athodec 99 e: ve y m ch longer; e h ensth orvhe eht- L.

.lfhezcathodetd theapresent:inventionis; of course; use.-. ful' in; .othenthan the particularhydrogen discharge X device before-a referred} to. It may, as by two further illus-- trations; be employed in gaseous diodes orthyratrons of 1 other construction. Other cathode-cup or base configurations and structures may also be employed. As before stated, in addition, it is not necessary that the vanes be of rectangular configuration as discussed in connection with the embodiments of Figs. 1 and 2. They may, for example, be of other configuration, such as in the form of the concentrically and coaxially disposed annular or cylindrical vanes 13, 15, 17 etc., Fig. 3, carried by the circular base member 11' containing therein the heater element 19 and supportedwithin the cylindrical'shield' 7 As another example, the vanes may be constructed in honey-comb form to provide still a greater efiective cathode-emission area. Such honey-combvane-units-are illustrated at 51. in Fig, 4.

Further modifications will occur to those skilled in the art and all suchare considered to-fall within the spirit and scope of the invention as defined in the appended claims.

Whatris-claimed is:

1. An electric-discharge device having a plurality. of electrodesincluding an anode anda cathode spacedfrom one another along a predetermined directionwithin an ionizablemedium, the cathode comprising a base member, carrying a plurality. of spaced vanes havingelectrom emitting surfaces extending: substantialiy. along the pre.

determined direction from the base member and extend ing substantially completely acrossthe base member, the anode having a. surface co-extensive with the complete plurality of cathode vanes for cooperating therewith, and means for. heating the base member.

2; An. electricedischarge device having a plurality of electrodes including an anode; and a cathodespacedfrom one another along a predetermined direction within an ionizable medium, thecathode comprising abase member carrying aplurality, of spaced. vanes having electronemitting. surfacesextending substantially-along'the predetermined direction from the, base member a distance less I than the other dimension of thevane surfaces and extending, substantially completely across, the. base member, the; anode having a surface co-extensive with the complete plurality, of cathode vanesfor cooperating therewith, and means for heating, thebase member.

3; An. electric-discharge, device having a plurality-of electrodes includingan anode and a cathode spaced from one another along a;- predetermined. directionwithin. an ionizable medium, the cathode comprising a basemember. carrying a plurality of;v spacedsubstantially rectangular; vanes having-electromemittingsurfaces ,extendingsubstantially along the predetermined direction from the base.

member and extending substantially completely across the. base member, the anode having a surface co -extensive with, the complete plurality of cathode vanes for cooperating therewith, and. means, for heating the base member.

4.-An electric-discharge device having a plurality. of.

electrodes includingan anodeand a;cathode spaced from one another along a predetermineddirection within an ionizable medium, the cathodecomprising a, base. member carrying a, plurality of, spaced annular vaneshayingelectron-emittingsurfaces extending substantially along; the.

predetermined direction from the base member andpex electrodes including. an anode and" a cathode spaced from,

one. another along aj predetermined direction within an ionizab1e= medium, thezcathode: comprisinga: base member carryin g a plurality. offsubstantially. concentricxcylin drical =vanes: hayingeleetromemitting" surfaces: extendipg substantially along the,predetermin ed1 direction frongthe; base member, and; extending; substantially. completely across the base member, the; anode having a surface coextensive with the complete plurality of cathode vanes for cooperating therewith, and means for heating the base member.

6. An electric-discharge device having a plurality of electrodes including an anode and a cathode spaced from one another along a predetermined direction within an ionizable medium, the cathode comprising a base member carrying a plurality of honey-comb-arranged vanes having electron-emitting surfaces extending substantially along the predetermined direction from the base member and extending substantially completely across the base member, the anode having a surface co-extensive with the complete plurality of cathode vanes for cooperating therewith, and means for heating the base member.

7. In an electric discharge device, a cathode comprising a base member carrying a plurality of substantially parallel thin cathode elements each having electron-emitting surfaces extending substantially completely across and extending normal to the base and separated from one another by a spacing of the order of substantially one-to-two millimeters.

8. In an electric discharge device, a cathode comprising a base member carrying a plurality of substantially parallel thin cathode elements each having electron-emitting surfaces extending substantially completely across and extending normal to the base and separated from one another by a spacing of the order of substantially one-to-two millimeters, and means for heating the base member.

9. A gaseous-discharge device having a plurality of electrodes including an anode and a cathode spaced from one another along a predetermined direction within a hydrogen-gas medium, the cathode comprising a base member carrying a plurality of spaced vanes having electron-emitting surfaces extending substantially along the predetermined direction from the base member and extending substantially completely across the base member, the anode having a surface co-extensive with the complete plurality of cathode vanes for cooperatnig therewith, and means for heating the base member.

10. An electric-discharge device having a plurality of electrodes including an anode and a cathode spaced from one another along a predetermined direction within an ionizable medium, the cathode comprising a base member carrying a plurality of spaced vanes having electronemitting surfaces extending substantially along the predetermined direction from the base member and extending substantially completely across the base member, the anode having a surface co-extensive with'the' complete plurality of cathode vanes for cooperating therewith, and means for heating the cathode.

11. in an electric-discharge device, a cup-shaped cathode containing a substantially fiat base member carrying a plurality of spaced conductive vanes having electronemitting surfaces extending in a direction toward the opening of the cup and extending substantially completely across the said opening, and means for heating the cathode.

'12. In an electric-discharge device, a cathode comprising a base member carrying a plurality of substantially planar sections each having electron-emitting substantially planar surfaces extending substantially normal to the base member and extending substantially completely across the base member.

13. In an electric-discharge device, a cathode comprising a base member carrying a plurality of substantially planar sections each having electron-emitting substantially planar surfaces extending substantially completely across the base member and extending substantially normal to the base a distance L given substantially by the equation where i is the current passed through the discharge device from the cathode, E is the electric field acting upon the cathode, V is the potential drop across the cathode sheath V is the potential gradient in the cathode sheath and P is the total perimeter of the cathode.

References Cited in the file of this patent UNITED STATES PATENTS 

